In recent years, higher efficiency in a cutting process of a metal material has increasingly been demanded and a higher cutting speed has been required. Therefore, improvement in heat resistance (oxidation resistance) or wear resistance has been demanded in a coating film covering a surface of a substrate of a cutting tool.
Accordingly, in order to meet such demands, development of a coating film has been conducted in various manners. For example, use of a compound having a specific composition containing Al and Cr (what is called an AlCr-based coating film) has been proposed for such a coating film (Japanese Patent National Publication No. 2006-524748 (Patent Document 1)). According to this proposal, heat resistance or wear resistance can be improved to some extent, however, brittleness, which is a problem specific to such an AlCr-based coating film, is exhibited, which gives rise to a problem of fracture and peel-off of the coating film itself due to impact or the like during cutting.
On the other hand, an attempt to improve heat resistance or wear resistance by using a compound having a specific composition containing Ti and Si for a coating film (what is called a TiSi-based coating film) has conventionally been made. Such a TiSi-based coating film again exhibits brittleness as in the AlCr-based coating film above, which leads to a problem of fracture or peel-off of the coating film itself. In order to solve such a problem, it has been proposed to alternately stacking a coating film composed of a compound having a specific composition containing Ti and Al (TiAl-based coating film) and such a TiSi-based coating film (Japanese Patent Laying-Open No. 2000-334606 (Patent Document 2)). Such a proposal, however, was not able to sufficiently prevent fracture or peel-off of the coating film itself under severe cutting conditions in some cases.
In contrast, improvement in brittleness by alternately stacking a plurality of layers having a specific composition containing Al and Si has been proposed (Japanese Patent Laying-Open No. 2006-137982 (Patent Document 3)). The layer containing Al and/or Si intrinsically tends to exhibit brittleness and the problem of fracture or peel-off of the coating film has not yet sufficiently been solved.
Patent Document 1: Japanese Patent National Publication No. 2006-524748
Patent Document 2: Japanese Patent Laying-Open No. 2000-334606
Patent Document 3: Japanese Patent Laying-Open No. 2006-137982